Stabilisation and mineralisation of sludge in reed bed system after years of operation

Size: px

Start display at page:

Download "Stabilisation and mineralisation of sludge in reed bed system after years of operation"

Brent Barnett
5 years ago
Views:

1 Stabilisation and mineralisation of sludge in reed bed system after years of operation Steen Nielsen a Eleonora Peruzzi b, Cristina Macci b, Serena Doni b, Grazia Masciandaro b a ORBICON, Ringstedvej 20, Roskilde, 4000, DENMARK, smni@orbicon.dk b CNR-ISE, via Moruzzi 1, Pisa, 56124, ITALY, grazia.masciandaro@ise.cnr.it The 13 th International Conference Wetland Systems for Water Pollution Control November 2012 Steen Nielsen - smni@orbicon.dk 23/11/2012 1

2 Investigation of stabilisation of sludges in three Danish STRBS: Helsinge, Nordborg and Nakskov. To evaluate the sludge quality after treatment in STRBS, comparing also the different pathways by which of stabilisation occurred. The efficiency in sludge stabilisation in the sludge residue within the STRBS after periods of operation between 9 21 years. Is it possible to hypothesise a connection between the sludge quality applied to the (STRBS) and different ways of stabilising (mineralisation or huminification) the sewage sludge accumulated in vertical profile. To achieve this purpose, parameters correlated to biochemical properties of organic sludge matter have been determined. Steen Nielsen - smni@orbicon.dk 23/11/2012 2

3 Danish references: Sludge Treatment System in Reed Beds Sludge Type (Helsinge): Mix of aerobic SAS/Conc. Anaerobic SAS Sludge Type (Nordborg): Mix of SAS/Digested primary sludge (Anaerobic) (Germany) Sludge Type (Nakskov): SAS (anaerobic) from sec. sedimen. tanks 3

4 Helsinge (STRBS) Basins : 10 Area load : kg ds/m²/yr Load/rest ratio : 40-60/4-7 days Acc. Rate : 0.12 m/yr. 23/11/2012 4

5 Nordborg (STRBS) Basins : 10 Area load : kg ds/m²/yr Load/rest ratio : 40-70/4-7 days Acc. Rate : 0.11 m/yr. Steen Nielsen - smni@orbicon.dk 23/11/2012 5

6 Nakskov (STRBS) Basins : 10 Area load : kg ds/m²/yr Load/rest ratio : 40-50/5-7 days Acc. Rate : 0.07 m/yr. Steen Nielsen - smni@orbicon.dk 23/11/2012 6

7 Waste water treatment plants (WWTP) and STRBS operations data (Helsinge) (Nordborg) (Nakskov) Population equivalent (PE.) 42,000 18,000 25,000 Sludge type Mix SAS/- Anaerobic SAS Mix SAS/Digested SAS Phosphorus removal PAX/Fe PAX/PIX PIX-118 Capacity (tons ds y -1 ) Quality (Feed Sludge) Dry Solid (%) % % % Loss on ignition (%) % 50-65% 45-60% Fat (mg/kg ds) 500-7, , ,000 Oil (mg/kg ds) 100-2, , Sludge Age (aerobic-days) Start of the operation period Total basin area (m 2 ) 10,500 (10 basins) 7,000 (10 basins) 9,920 (10 basins) Basin area (m 2 ) 1, ,308 Loading rate (kg ds m -2 y -1 ) Dim Loading rate (kg ds m -2 y -1 ) - Real Loading/Resting (days) 4-7/ / /40-50 Resting period (months) before emptying Emptying period (all basins) and 2011, Sludge height at the emptying period (cm) Quality (Sludge residue) Fat (mg/kg ds) App , Oil (mg/kg ds) , Loss on ignition (%) 40-50% 40-55% 40-55% Steen Nielsen - smni@orbicon.dk 23/11/2012 7

$Separated in approximately 10-cm depth fractions.$

8 Sampling 1-4 in sites in 1basin were randomly selected within each of the 3 the STRBS. Samples were collected by a 3-cm diameter stainless steel corer. Separated in approximately 10-cm depth fractions. Samples from the same depth were pooled and mixed Sampling after one entire cycle of full operation: Nakskov Nordborg Helsinge May 2011 June 2011 August 2008 Basin no. 3 Basin no. 3 Basin no months after the last load 3 months after the last load 4 months after the last load Profile: 150 cm Profile: 90 cm Profile: 150 cm The deepest sludge residue layers (layer 8 to 10) are between 9 and 21 years old. Steen Nielsen - smni@orbicon.dk 23/11/2012 8

9 Nordborg (STRBS) Total organic carbon (% C) : Decreased Water soluble carbon (mg c/kg ds h) : Decreased β-glucosidase activity (mg PNP/kg ds h) : Decreased Total nitrogen (% N) N-NH3 (mg N/kg ds) Urease activity (mg NH4+/kg ds h) :Decreased : Decreased : Decreased Steen Nielsen - smni@orbicon.dk 23/11/2012 9

10 Helsinge (STRBS) Total organic carbon (% C) : Decreased Water soluble carbon (mg c/kg ds h) : Decreased β-glucosidase activity (mg PNP/kg ds h) : Decreased Total nitrogen (% N) N-NH3 (mg N/kg ds) Urease activity (mg NH4+/kg ds h) :Decreased : Decreased : Stable Steen Nielsen - smni@orbicon.dk 23/11/

11 Nakskov (STRBS) Total organic carbon (% C) : Unchanged Water soluble carbon (mg c/kg ds h) : Decreased β-glucosidase activity (mg PNP/kg ds h) : Decreased Total nitrogen (% N) N-NH3 (mg N/kg ds) Urease activity (mg NH4+/kg ds h) :Unchanged : Decreased : Decreased Steen Nielsen - smni@orbicon.dk 23/11/

12 Humic substances characterisation (1) The level of humic carbon (FA+HA) decreased with increasing depths - suggesting that a mineralisation process was still occurring. PEC: The increase with increasing depth indicated that the process of humification was successful in stabilizing organic matters As the labile organic matter had been decomposed with increasing depth - the humification process had started in stabilising the organic matter with the synergic action of plant and microorganisms. Helsinge Nordborg Nakskov Layer FA (mg C/kg ds) 26662b 18720a 19686a 25374b 19364a 16574a 12603a 18184b 11852a HA (mg C/kg ds) 13200b 8371a 7834a 4722a 4185a 6868b 4185a 3756a 7083b PEC (mg C/kg ds) 9430b 8759ab 8306a 7146a 7135a 7019a 7745a 7088a 12319b PEC/WSC 2.21a 5.07b 4.53b 2.53a 5.08b 5.79b 1.36a 5.38b 6.80c β-gluc ex (mg PNP/kg ds) 14.3ab 19.0b 10.5a 12.8a 17.3a 12.2a 16.7b 10.4ab 6.8a Urease ex (mg NH 4+ /kg ds h) 9.37b 6.06a 7.37ab 6.22a 5.86a 6.08a 7.78b 5.42a 5.03a Different letters (a, b, c) mean values significantly different (P<0.05) between layers within each STRBS. Decreased Increased Unchanged Achieved heigh values Throughout the entire profile, fulvic acids (FA) and humic acids (HA) seemed to be inversely correlated: FA reduced with increasing depth, the HA raised to high concentrations Steen Nielsen - smni@orbicon.dk 23/11/

13 Humic substances characterisation (2) These results are also confirmed by the trend of PEC/WSC ratio, which increased significantly in the deepest layers. The level of humic-enzyme complexes (extracellular b-glucosidase and urease enzymes) reached high values in all STRBSs Demonstrating that a significant nucleus of humic-enzyme complexes resistant to microbial and environmental action were formed during the stabilisation process Helsinge Nordborg Nakskov Layer FA (mg C/kg ds) 26662b 18720a 19686a 25374b 19364a 16574a 12603a 18184b 11852a HA (mg C/kg ds) 13200b 8371a 7834a 4722a 4185a 6868b 4185a 3756a 7083b PEC (mg C/kg ds) 9430b 8759ab 8306a 7146a 7135a 7019a 7745a 7088a 12319b PEC/WSC 2.21a 5.07b 4.53b 2.53a 5.08b 5.79b 1.36a 5.38b 6.80c β-gluc ex (mg PNP/kg ds) 14.3ab 19.0b 10.5a 12.8a 17.3a 12.2a 16.7b 10.4ab 6.8a Urease ex (mg NH 4+ /kg ds h) 9.37b 6.06a 7.37ab 6.22a 5.86a 6.08a 7.78b 5.42a 5.03a Different letters (a, b, c) mean values significantly different (P<0.05) between layers within each STRBS. Decreased Increased Unchanged Achieved heigh values Steen Nielsen - smni@orbicon.dk 23/11/

14 PC 2 Principal component analysis (PCA) Principal component loadings. The PCA of the data set indicated that the 62.0% of the data variance a) as being contained in two components. *parameters b) used for PCA interpretation PC 1 PC 2 Total Organic Carbon Total Nitrogen * Water Soluble Carbon N-NH * -glucosidase 0.81* Urease 0.84* 0.10 Fulvic Acids Humic Acids * PEC -0.81* glucosidase ex 0.74* 0.25 Urease ex * Prp.Tot Steen Nielsen - smni@orbicon.dk Nordborg On PC 2 Helsinge are significant with the same sign (+) the TN, N-NH3, HA and extracellular Nakskov urease activity. This means that all these 7 parameters are positevely 9 correlated and have the same behaviour -3,0-1,5 (when one of these parameters increase, also the 10 other increase, and viceversa). 8 23/11/

15 Principal component analysis (NORDBORG): Biplot of scores and loadings (PC 1 linket to Huminification vs PC 2 linket to Mineralisation). The samples shifted on PC 1 and PC2. Humification and mineralization processes are present in the same level. With increasing depth, the layers were shifted from the top right to the bottom left of the plot. Suggesting equilibrium in mineralisation and humification processes. Steen Nielsen - smni@orbicon.dk 23/11/

16 Principal component analysis (HELSINGE): Biplot of scores and loadings (PC 1 linket to Huminification vs PC 2 linket to Mineralisation). The samples shifted only across PC 2, from the top to the bottom of the plot, highlighting the decrease with increasing depth of all parameters linked to N cycle. Clearly linked to mineralisation process, which has involved not only the easily degradable compounds, but also the more stabilised. This fact means that in the surface layers, the content of TN, N-NH3, HA and extracellular urease activity is higher with respect to the deepest layers. The process of mineralization seemed to have interested not only : the easily degradable organic matter (decrease of TN and N-NH3 from the surface to the depth) but also the humic acids (HA), which represent the more stable forms of organic matter. Decrease of HA means an high level of mineralization High content of TN and N-NH3 mean a high degree of mineralization Steen Nielsen - smni@orbicon.dk 23/11/

17 Principal component analysis (NAKSKOV): Biplot of scores and loadings (PC 1 linket to Huminification vs PC 2 linket to Mineralisation). Clearly associated to the humification process. the layers were shifted along the PC1 With increasing depth, the layers were shifted along the PC1, from the right to the left, thus highlighting the decrease of total enzymatic activities and the increase in PEC. PEC increase means high level of humification Low level of total enzymatic activities means low level of mineralization process. Comment: On PC 1 are significant the B-Gluc activity, the urease activity, the extracellular B Gluc (all with + sign), and the PEC (with sign). This fact means that where the b-glucosidase activities and the urease activities are higher, the PEC is lower, and viceversa (total and extra b-gluc activities and total urease activity, are negatively correlated) For what concern the Nakskov samples, they shifted from right to left across PC 1 and they don t change on PC 2, so this RBS is more influenced by the parameters that are significant on PC 1. The layers of Nakskov samples shifted form right to left as their depth, so the surface layers are in the right of the plot, while the deepest are in the left. This fact means that the surface layers are characterized by higher level of enzymatic activities and low level of PEC, while the deepest layers ar characterized by low level of enzymatic activities and a higher level of PEC. Steen Nielsen - smni@orbicon.dk 23/11/

18 Conclusions (1 2) Stabilisation of sludges was investigated in three different Danish STRBSs (Helsinge, Nordborg, Nakskov). The study demonstrated the successful stabilisation of organic matter in the three systems. The quality of sludge applied did not affect the process of stabilisation, even though different pathways were followed. On the basis of the biochemical characterisation of sludge residue It is, in fact, possible to firmly establish a connection between the sludge quality applied (deriving from different treatment aerobic and/or anaerobic processes) to the STRBSs and the different pathways of organic matter stabilsation (humification and/or mineralisation processes). Steen Nielsen - smni@orbicon.dk 23/11/

19 Conclusions (2 2) The presence/absence of anaerobic sludge seemed to have a considerable influence on the stabilisation occurring in the STRBSs: In the case of: Aerobic sludges, the humification process will be prevalent Anaerobic sludges, the mineralisation process is likely to override the other processes of stabilisation. The STRB is, if the system has the right dimensioning, design and operation in relation to the sludge quality, a feasible technology for sludge treatment and stabilisation before its final land disposal. Steen Nielsen - smni@orbicon.dk 23/11/

20 THANK YOU FOR YOUR ATTENTION ACKNOWLEDGEMENTS Thanks to the different partners involved in this study: CNR- ISE - National Research Council Istitute for Ecosystem Study Pisa Grazia Masciandaro Eleonora Peruzzi Steen Nielsen - smni@orbicon.dk 23/11/

Lecture 19: Soil Organic Matter

Lecture 19: Soil Organic Matter Effects of OM Properties on Soil Property Dark color Excellent water retention Binds to clay minerals Metal chelation Low water solubility ph buffering High CEC Nutrient